Wellington: A storm the size of Australia whipped New Zealand on Saturday leaving tens of thousands of people without power and sending a stadium roof crashing down.

The second natural disaster to hit the country in a fortnight lifted roofs and uprooted trees as hurricane-force winds swept across the country and lightning strikes ignited fires.

The South Island city of Christchurch escaped the worst of the storm but continued to be rocked up a series of aftershocks up to magnitude 4.5 two weeks after a 7.0 earthquake caused billions of dollars worth of damage.

The storm, described by the independent weatherwatch.co.nz website as "one of the largest storms on the planet" and covering an area the size of Australia stretched emergency services as it wreaked havoc across the country

"Most of the calls were about fallen trees across roads or property, and roofs lifting," said Steve Smith of the Fire Service northern communications centre.

Nearly 100,000 people lost electricity supplies overnight Friday and by Saturday afternoon 17,000 were still waiting to be reconnected.

Winds reached hurricane force on the coast west of the main city of Auckland, said weatherwatch head analyst Philip Duncan as gusts up to 154 kilometres (96 miles) per hour swept in from the Tasman Sea.

In the lower North Island, there were more than 100 lightning, sparking fires in at least one building and several trees.

In the Manawatu district north of Wellington flooding made roads impassable.